A Salt-Templated Synthesis Method for Porous Platinum-based Macrobeams and Macrotubes

Summary

A synthesis method to obtain porous platinum-based macrotubes and macrobeams with a square cross section through chemical reduction of insoluble salt-needle templates is presented.

Abstract

The synthesis of high surface area porous noble metal nanomaterials generally relies on time consuming coalescence of pre-formed nanoparticles, followed by rinsing and supercritical drying steps, often resulting in mechanically fragile materials. Here, a method to synthesize nanostructured porous platinum-based macrotubes and macrobeams with a square cross section from insoluble salt needle templates is presented. The combination of oppositely charged platinum, palladium, and copper square planar ions results in the rapid formation of insoluble salt needles. Depending on the stoichiometric ratio of metal ions present in the salt-template and the choice of chemical reducing agent, either macrotubes or macrobeams form with a porous nanostructure comprised of either fused nanoparticles or nanofibrils. Elemental composition of the macrotubes and macrobeams, determined with x-ray diffractometry and x-ray photoelectron spectroscopy, is controlled by the stoichiometric ratio of metal ions present in the salt-template. Macrotubes and macrobeams may be pressed into free standing films, and the electrochemically active surface area is determined with electrochemical impedance spectroscopy and cyclic voltammetry. This synthesis method demonstrates a simple, relatively fast approach to achieve high-surface area platinum-based macrotubes and macrobeams with tunable nanostructure and elemental composition that may be pressed into free-standing films with no required binding materials.

Introduction

Numerous synthesis methods have been developed to obtain high surface area, porous platinum-based materials primarily for catalysis applications including fuel cells¹. One strategy to achieve such materials is to synthesize monodisperse nanoparticles in the form of spheres, cubes, wires, and tubes^2,3,4,5. To integrate the discrete nanoparticles into a porous structure for a functional device, polymeric binders and carbon additives are often required^6,7. This s....

Protocol

CAUTION: Consult all relevant chemical safety data sheets (SDS) before use. Use appropriate safety practices when performing chemical reactions, to include the use of a fume hood and personal protective equipment. Rapid hydrogen gas evolution during electrochemical reduction can cause high pressure in reaction tubes causing caps to pop and solutions to spray out. Ensure that reaction tube caps remain open as specified in the protocol. Conduct all electrochemical reductions in a fume hood.

1. Magnus’ salt derivatives template preparation

NOTE: All salt templates should be chemically reduced within a few hours ....

Results

The addition of oppositely charged square planar noble metal ions results in near instantaneous formation of high aspect ratio salt crystals. The linear stacking of square planar ions is shown schematically in Figure 1, with the polarized optical microscopy images revealing salt needles that are 10’s to 100’s of micrometers long. A concentration of 100 mM was used for all platinum, palladium, and copper salt solutions. While the salt needle templates are charge neutral in that th.......

Discussion

This synthesis method demonstrates a simple, relatively fast approach to achieve high-surface area platinum-based macrotubes and macrobeams with tunable nanostructure and elemental composition that may be pressed into free-standing films with no required binding materials. The use of Magnus’ salt derivatives as high aspect ratio needle shaped templates provides the means to control resulting metal composition through salt-template stoichiometry, and when combined with choice of reducing agent, control over the nano.......

Materials

Name	Company	Catalog Number	Comments
50 mL Conical Tubes	Corning Costar Corp.	430290
Ag/AgCl Reference Electrode	BASi	MF-2052
Cu(NH3)4SO4Ÿ•H2O	Sigma-Aldrich	10380-29-7
dimethylamine borane (DMAB)	Sigma-Aldrich	74-94-2
K2PtCl4	Sigma-Aldrich	10025-99-7
Miccrostop Lacquer	Tober Chemical Division	NA
Na2PdCl4	Sigma-Aldrich	13820-40-1
NaBH4	Sigma-Aldrich	16940-66-2
Polarized Optical Microscope	AmScope	PZ300JC
Potentiostat	Biologic-USA	VMP-3	Electrochemical analysis-EIS, CV
Pt wire electrode	BASi	MF-4130
Pt(NH3)4Cl2Ÿ•H2O	Sigma-Aldrich	13933-31-8
Scanning Electron Microscope	FEI	Helios 600	EDS performed with this SEM
Shelf Rocker	Thermo Scientific	Vari-Mix™ Platform Rocker
Snap Cap Microcentrifuge Tubes, 1.7 mL	Cole Parmer	UX-06333-60
X-ray diffractometer	PanAlytical	Empyrean	X-ray diffractometry
X-ray photoelectron spectrometer	ULVAC PHI - Physical Electronics	VersaProbe III